1. Field of the Invention
This invention relates to an analog/digital converter.
2. Discussion of Background
A prior art analog/digital converter is known, for example, from U.S. Pat. No. 4,296,412.
A/D converters are needed, particularly for electronic current transformers, which, apart from a brief "data refresh" so that the phase errors are kept small, also require a very wide dynamic range. In a combined converter for measuring and protection purposes (for example IEC class 0.2 in conjunction with IEC class 5P30), a dynamic range of up to 20 bits can be required.
The rapid "data refresh" can be achieved by tracking according to the above-noted U.S. Pat. No. 4,296,412 or also according to a circuit described and illustrated in Swiss Patent Application No. 10628/84 of Mar. 30, 1980 by the applicant.
The dynamic range of the analog/digital converter according to U.S. Pat. No. 4,296,412 is restricted by the number of digits at the output of the digital integrator or at the input of the digital/analog converter used for feedback, on the one hand, and by the demands on the accuracy of conversion of the input signal, on the other hand, even if the such demands apply only to a part of the range swept by the input signal.
It has also been proposed to expand the dynamic range of a tracking-type A/D converter arbitrarily by using several tracking loops. However, this method has the disadvantage that some analog components such as, for example, D/A converters and voltage comparators (or complete sets of window discriminators, since preferably tracking loops having an increased tracking rate are used) are repeated several times in the whole A/D converter.